System and method for passive optical network communication

ABSTRACT

In one embodiment, a method for passive optical network (PON) communication includes broadcasting, by an optical line terminal (OLT), a first message including a first start time of a first quiet window and a first allocation identification number (Alloc-ID), where the first Alloc-ID indicates a first supported upstream line rate associated with the first quiet window. The method also includes receiving, by the OLT from a first optical network unit (ONU) during the first quiet window, a first serial number response, wherein a first transmitting upstream line rate of the first ONU is equal to the first supported upstream line rate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims is a continuation of U.S. application Ser. No.14/071,005, filed on Nov. 4, 2013, which claims the benefit of U.S.Provisional Application Ser. No. 61/722,460 filed on Nov. 5, 2012, whichapplications are hereby incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a system and method for opticalcommunications, and, in particular, to a system and method for passiveoptical network communication.

BACKGROUND

A passive optical network (PON) is a point-to-multipoint, fiber to thepremises fiber-optic access network architecture in which unpoweredoptical splitters are used to facilitate a single optical fiber to servemultiple premises. For example, a single optical fiber may serve 16-128premises. A PON may reduce the amount of optical fiber and centraloffice equipment compared to point-to-point architectures. A PON mayinclude an optical line terminal (OLT) at the service provider's centraloffice and a number of optical network units (ONUs) near end users.Downstream signals are broadcast to the premises sharing multiple fiberswith encryption to prevent eavesdropping.

A PON uses wavelength division multiplexing (WDM), using one wavelength,for example 1490 nm, for downstream traffic and another wavelength, forexample 1310 nm, for upstream traffic. A 1550 nm wavelength is used foroptional overlay services, for example radio frequency (RF) analogvideo.

SUMMARY

An embodiment method for passive optical network (PON) communicationincludes broadcasting, by an optical line terminal (OLT), a firstmessage including a first start time of a first quiet window and a firstallocation identification number (Alloc-ID), where the first Alloc-IDindicates a first supported upstream line rate associated with the firstquiet window. The method also includes receiving, by the OLT from afirst optical network unit (ONU) during the first quiet window, a firstserial number response, wherein a first transmitting upstream line rateof the first ONU is equal to the first supported upstream line rate.

Another embodiment method for passive optical network (PON)communication includes receiving, by an optical network unit (ONU) froman optical line terminal (OLT), a first message including a first starttime of a first quiet window and a first allocation identificationnumber (Alloc-ID), where the first Alloc-ID indicates a first supportedupstream line rate associated with the first quiet window. The methodalso includes when a transmitting upstream line rate of the ONU is equalto the first supported upstream line rate, transmitting, by the ONU tothe OLT during the first quiet window, a first serial number responseand when the transmitting upstream line rate of the ONU is not equal tothe first supported upstream line rate, not transmitting, by the ONU tothe OLT during the first quiet window.

An embodiment optical line terminal (OLT) includes a processor and acomputer readable storage medium storing programming for execution bythe processor, the programming including instructions to broadcast afirst message including a first start time of a first quiet window, anda first allocation identification number (Alloc-ID), where the firstAlloc-ID indicates a first supported upstream line rate associated withthe first quiet window. The programming also includes instructions toreceive, from an optical network unit (ONU) during the first quietwindow, a first serial number response, where a transmitting upstreamline rate of the ONU is equal to the first supported upstream line rate.

An embodiment optical network unit (ONU) includes a processor and acomputer readable storage medium storing programming for execution bythe processor, the programming including instructions to receive, froman optical line terminal (OLT), a first message including a first starttime of a first quiet window and a first allocation identificationnumber (Alloc-ID), where the first Alloc-ID indicates a first supportedupstream line rate associated with the first quiet window. Theprogramming also includes instructions to, when a transmitting upstreamline rate of the first ONU is equal to the first supported upstream linerate, transmit, to the OLT during the first quiet window, a first serialnumber response, and when the transmitting upstream line rate of the ONUis not equal to the first supported upstream line rate, not transmit, bythe ONU to the OLT during the first quiet window.

The foregoing has outlined rather broadly the features of an embodimentof the present invention in order that the detailed description of theinvention that follows may be better understood. Additional features andadvantages of embodiments of the invention will be describedhereinafter, which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiments disclosed may be readily utilized as a basisfor modifying or designing other structures or processes for carryingout the same purposes of the present invention. It should also berealized by those skilled in the art that such equivalent constructionsdo not depart from the spirit and scope of the invention as set forth inthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawing, in which:

FIG. 1 illustrates a diagram of an embodiment passive optical network(PON) for communicating data;

FIG. 2 illustrates a diagram of another embodiment PON for communicatingdata;

FIG. 3 illustrates a diagram of an embodiment message stream between anoptical line terminal (OLT) and an optical network unit (ONU);

FIG. 4 illustrates a flowchart of an embodiment method for activatingONUs performed by an OLT;

FIG. 5 illustrates a flowchart of an embodiment method for activatingONUs performed by an ONU; and

FIG. 6 illustrates a block diagram of an embodiment general-purposecomputer system.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the embodiments andare not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

It should be understood at the outset that although an illustrativeimplementation of one or more embodiments are provided below, thedisclosed systems and/or methods may be implemented using any number oftechniques, whether currently known or in existence. The disclosureshould in no way be limited to the illustrative implementations,drawings, and techniques illustrated below, including the exemplarydesigns and implementations illustrated and described herein, but may bemodified within the scope of the appended claims along with their fullscope of equivalents.

Passive optical networks (PONs), such as a gigabit PON (G-PON) and a 10gigabit PON (XG-PON), are point-to-multipoint optical networks. In anexample, G-PON supports 1.25 G upstream lines, while XG-PON supports 2.5G upstream lines. Dynamic bandwidth allocation (DBA) may be used tosupport a higher bandwidth for G-PON and XG-PON.

An example PON supports different upstream line rates for differentoptical network units (ONUs). An optical line terminal (OLT) opens updifferent quiet windows for different upstream line rates. Then, ONUsrespond during the appropriate quiet window for their upstream linerate.

FIG. 1 illustrates G-PON 100, which may be operated at a variableupstream line rate. For example, G-PON 100 supports upstream line ratesof 1.25 G and 2.5 G. Central office 102 contains OLT 108, which iscoupled to ONUs 112. Five ONUs are pictured, but fewer or more ONUs maybe used. OLT 108 contains transmitter 104 and receiver 106. Transmitter104 transmits data at 2.5 G, while receiver 106 receives data at 1.25 Gand 2.5 G. Fiber 109 couples OLT 108 to splitter 110. Then, fibers infan out from splitter no to ONUs 112, with one fiber connecting an ONUto splitter 110. ONUs 112 contain receivers 114 and transmitters 116.Receivers 114 receive data at 2.5 G, while transmitters 116 transmit atvarious rates. Some transmitters 116 transmit data at 1.25 G, whileother transmitters 116 transmit data at 2.5 G.

FIG. 2 illustrates XG-PON 120, which operates at a variable upstreamline rate. For example, XG-PON 120 supports ONUs with upstream linerates of 2.5 G and 10 G. Central office 122 contains OLT 128, which iscoupled to ONUs 132. OLT 128 contains transmitter 124, which transmitsat 10 G and receiver 126, which receives data at 2.5 G and 10 G. Fiber129 couples OLT 128 to splitter 130. Splitter 130 is coupled to ONUs 132by fibers 131, which fan out from splitter 1030. ONUs 132 containreceivers 134 and transmitters 136. Receivers 134 receive data at 10 G,while transmitters 136 transmit data at 2.5 G or 10 G. In an example,the 10 G upstream channel is used for business customers, while the 2.5G upstream channel is used by residential customers.

An embodiment supports multiple upstream rates in G-PON and XG-PON byenhancing the PON operation, administration, and maintenance (OAM)channel to provide different ranging grants to new ONUs with differentupstream rates. The OLT opens separate quiet windows for ONUs withdifferent upstream rates by broadcasting different serial numbergrants/requests. This enhancement of the ONU activation processfacilitates the OLT to identify the ONU upstream rates and group ONUsbased on upstream rate.

FIG. 3 illustrates message diagram 150 for messages exchanged betweenOLT 152 and ONU 154 during the activation procedure. During activation,an inactive ONU joins or resumes operation on the PON. Initially, OLT152 broadcasts a downstream (DS) physical layer (PHY) frame containing aphysical synchronization block appropriation for downstream (PSBd) and aPHY frame content. The PSBd contains a serial number (SN) grant message.The SN Grant message contains an allocation identification number(Alloc-ID), a start size, and a grant size. Alloc-ID is a logical ID. Inmessage diagram 150, Alloc-ID is 1023, the start time is S, and thegrant size is 0. ONU 154 receives the SN Grant message.

At the start time S, the OLT opens a quiet window. During the quietwindow, ONUs already registered with OLT 152 do not communicate with OLT152. Also, during the quiet window, ONU 154 transmits a serial numberresponse containing an upstream (US) PHY frame having a physicalsynchronization block appropriation for upstream (PSBu) and a physicallayer operation, administration, and maintenance (PLOAM). During thequiet window, multiple ONUs may associate with the PON.

In an embodiment, there are multiple quiet windows, where each quietwindow is for ONUs with a particular upstream line rate to use. TheAlloc-ID indicates the upstream line rate for a given quiet window.Then, only ONUs with the designated upstream line rate associate duringthe quiet window. Table 1 below illustrates embodiment G-PON Alloc-IDvalues. The G-PON Alloc-ID is 12 bits. Some of the Alloc-IDs are used torepresent serial number grants for ONUs with an upstream rate differentfrom 1.25 G. Alloc-IDs from 0 to 251 are default Alloc-IDs, implicitlyassigned with, and equal to the ONU identification number (ID). AnAlloc-ID of 252, which is broadcast, is used by the OLT in a serialnumber grant allocation structure to indicate that any ONU with anyupstream line rate executing the serial number acquisition phase of theactivation procedure may use this allocation to transmit a serial numberresponse. On the other hand, an Alloc-ID 253, which is broadcast, isused by an OLT in a serial number grant allocation structure to indicatethat any ONU with a 2.5 G upstream rate executing the serial numberacquisition phase of the activation procedure may use this allocation totransmit a serial number response. An Alloc-ID of 254, which isbroadcast, is used by the OLT in a serial number grant allocationstructure to indicate that any ONU with a 1.25 G upstream rate executingthe serial number acquisition phase of the activation procedure may usethis allocation to transmit a serial number response. Alloc-ID 255 isunassigned, and Alloc-IDs 256 to 4095 are assignable. When more than asingle Alloc-ID is needed for an ONU, the OLT assigns additionalAlloc-IDs to that ONU by selecting a unique number from this range.

TABLE 1 Alloc-ID Designation Comment 0 . . . 251 Default DefaultAlloc-ID, which is implicitly assigned with and is equal to the ONU-ID.252 Broadcast Used by OLT in a serial number grant allocation structureto indicate that any ONU supporting either 1.25 G or 2.5 G upstream linerate which executes the serial number acquisition phase of theactivation procedure may use this allocation to transmit a serial numberresponse. 253 Broadcast Used by OLT in a serial number grant allocationstructure to indicate that any ONU supporting a 2.5 G upstream line ratewhich executes the serial number acquisition phase of the activationprocedure may use this allocation to transmit a serial number response.254 Broadcast Used by OLT in a serial number grant allocation structureto indicate that any ONU supporting a 1.25 G upstream line rate whichexecutes the serial number acquisition phase of the activation proceduremay use this allocation to transmit a serial number response. 255unassigned 256 . . . 4095 Assignable If more than a single Alloc-ID isneeded for an ONU, the OLT assigns additional Alloc-IDs to that ONU byselecting a unique number from this range.

The quiet windows for different types of ONUs are scheduled in separatetimeslots, so that, as soon as the OLT receives a serial number ONUPLOAM, the transmitting upstream line rate of the ONU can be immediatelyidentified. For example, a quiet window with an Alloc-ID of 252indicates an ONU with an upstream rate of either 1.25 G or 2.5 G mayregister during the given quiet window, an Alloc-ID of 253 indicates anONU with an upstream rate of 2.5 G may register during the given quietwindow, and an Alloc-ID of 254 indicates an ONU with an upstream rate of1.25 G may register during the given quiet window.

Table 2 below indicates an example of Alloc-ID values for XG-PON.Alloc-IDs of 0 to 1020 are default Alloc-IDs that are implicitlyassigned with and equal to the ONU-ID. Alloc-IDs of 1021, 1022, and 1023are broadcast. An Alloc-ID of 1021 is used by an OLT in a serial numbergrant allocation structure to indicate that any upstream rate executingthe serial number acquisition phase of the activation procedure may usethis allocation to transmit a serial number response. On the other hand,an Alloc-ID of 1022 is used by an OLT in a serial number grantallocation structure to indicate that any ONU with a 10 G upstream rateexecuting the serial number acquisition phase of the activationprocedure may use this allocation to transmit a serial number response.An Alloc-ID of 1023 is used by an OLT in a serial number grantallocation structure to indicate that any ONU with a 2.5 G upstream rateexecuting the serial number acquisition phase of the activationprocedure may use this allocation to transmit a serial number response.Alloc-IDs of 1024 to 16383 are assignable. If more than a singleAlloc-ID is needed for an ONU, the OLT assigns additional Alloc-IDs tothat ONU by selecting a unique number from this range and communicatingit to the ONU using the Assign_Alloc-ID PLOAM message.

TABLE 2 Alloc-ID Designation Comment 0 . . . 1020 Default DefaultAlloc-ID, which is implicitly assigned with and is equal to the ONU-ID.1021 Broadcast Used by OLT in a serial number grant allocation structureto indicate that any ONU supporting either 10 G or 2.5 G any upstreamline rate which execute the serial number acquisition phase of theactivation procedure may use this allocation to transmit a serial numberresponse. 1022 Broadcast Used by OLT in a serial number grant allocationstructure to indicate that any ONU supporting 10 G upstream line ratewhich execute the serial number acquisition phase of the activationprocedure may use this allocation to transmit a serial number response.1023 Broadcast Used by OLT in a serial number grant allocation structureto indicate that any ONU supporting a 2.5 G upstream line rate whichexecute the serial number acquisition phase of the activation proceduremay use this allocation to transmit a serial number response. 1024 . . .16383 Assignable If more than a single Alloc-ID is needed for an ONU,the OLT assigns additional Alloc-IDs to that ONU by selecting a uniquenumber from this range and communicating it to the ONU using theAssign_Alloc-ID PLOAM message.

FIG. 4 illustrates flowchart 160 for an embodiment method of activatingONUs with different upstream line rates performed by an OLT. Initially,in step 162, the OLT determines the Alloc-ID for a quiet window. TheAlloc-ID indicates the upstream line rate of the ONUs that activateduring the quiet window. For example, in a G-PON, an Alloc-ID of 252indicates that any ONU may associate in the quiet window, an Alloc-ID of253 indicates that ONUs with upstream line rates of 2.5 G may respond inthis quiet window, and an Alloc-ID of 254 indicates that ONUs withupstream line rates of 1.25 G may respond in this quiet window. Inanother example, in an XG-PON, an Alloc-ID of 1021 indicates than anyONU may respond during this quiet window, an Alloc-ID of 1022 indicatesthat ONUs with upstream line rates of 10 G may respond during this quietwindow, and an Alloc-ID of 1023 indicates that ONUs with upstream linerates of 2.5 G may respond during this quiet window.

Next, in step 164, the OLT broadcasts a message containing the Alloc-IDdetermined in step 162 to multiple ONUs. In an example, the messagecontains a PSBd and a PHY frame content. The PSBd contains an SN Grantcontaining the Alloc-ID, the start time, and the grant size.

After broadcasting the message, the OLT begins the quiet window thestart time contained in the message in step 166. During the quietwindow, the OLT listens for messages from ONUs trying to associate withthe PON. During the quiet window, only ONUs with upstream line ratesindicated by Alloc-ID respond. Thus, the OLT knows the upstream linerate of ONUs that associate during this quiet window.

In step 168, the OLT receives a serial number response from an ONUseeking to activate. The OLT knows the upstream line rate of the ONUbased on the quiet window that the ONU uses. The serial number responsemay contain a PSBu and a PLOAM.

Then, in step 172, the OLT determines whether there is more time in thisquiet window. When there is time remaining in the quiet window, the OLTlistens for more messages for ONUs. When it receives a message, itproceeds to step 168. When the quiet window expires, the OLT proceeds tostep 174. In step 174, the ONU is associated with the PON, and the ONUand OLT privately communicate. The OLT transmits messages to the ONU andreceives messages from the ONU.

This procedure may be performed for a new quiet window. The new quietwindow may have the same upstream line rate or a different upstream linerate.

FIG. 5 illustrates flowchart 180 for a method of activating ONUsperformed by an ONU. Initially, in step 182, the ONU receives a messagecontaining an Alloc-ID. For example, the message contains a PSBd and aPHY frame content, and the PSBd contains an SN grant. The SN grantcontains an Alloc-ID, a start time, and a grant size. The Alloc-IDindicates the upstream line rates of ONUs that may respond during thequiet window, and the start time indicates the start time of the quietwindow. For example, in a G-PON, an Alloc-ID of 252 indicates that anyONU may respond in the quiet window, an Alloc-ID of 253 indicates thatONUs with upstream rates of 2.5 G may respond in this quiet window, andan Alloc-ID of 254 indicates that ONUs with upstream rates of 1.25 G mayrespond in this quiet window. In another example, in an XG-PON, anAlloc-ID of 1021 indicates than any ONU may associate in this quietwindow, an Alloc-ID of 1022 indicates that ONUs with upstream line ratesof 10 G may respond in this quiet window, and an Alloc-ID of 1023indicates that ONUs with upstream line rates of 2.5 G may respond inthis quiet window.

The ONU will only use the quiet window when the ONU has an upstream linerate compatible with the upstream line rate indicated by the Alloc-IDreceived in step 182. The ONU determines whether the quiet window has anupstream line rate that is the same as the ONU's upstream line rate. Ifthe upstream line rate of the quiet window is the same as that of theONU, the ONU determines the start time of the quiet window from themessage received in step 182.

During the quiet window for which the ONU has the appropriate upstreamline rate, in step 188, the ONU transmits a serial number response tothe OLT containing a PSBu and a PLOAM to associate with the PON.

Finally, in step 190, the ONU is associated with the PON. The ONU andthe OLT communicate privately. The ONU transmits messages to the ONU andreceives messages from the OLT.

FIG. 6 illustrates a block diagram of processing system 270 that may beused for implementing the devices and methods disclosed herein, such asby providing data to or from an OLT or ONU. Specific devices may utilizeall of the components shown, or only a subset of the components, andlevels of integration may vary from device to device. Furthermore, adevice may contain multiple instances of a component, such as multipleprocessing units, processors, memories, transmitters, receivers, etc.The processing system may comprise a processing unit equipped with oneor more input devices, such as a microphone, mouse, touchscreen, keypad,keyboard, and the like. Also, processing system 270 may be equipped withone or more output devices, such as a speaker, a printer, a display, andthe like. The processing unit may include central processing unit (CPU)274, memory 276, mass storage device 278, video adapter 280, and I/Ointerface 288 connected to a bus.

The bus may be one or more of any type of several bus architecturesincluding a memory bus or memory controller, a peripheral bus, videobus, or the like. CPU 274 may comprise any type of electronic dataprocessor. Memory 276 may comprise any type of system memory such asstatic random access memory (SRAM), dynamic random access memory (DRAM),synchronous DRAM (SDRAM), read-only memory (ROM), a combination thereof,or the like. In an embodiment, the memory may include ROM for use atboot-up, and DRAM for program and data storage for use while executingprograms.

Mass storage device 278 may comprise any type of storage deviceconfigured to store data, programs, and other information and to makethe data, programs, and other information accessible via the bus. Massstorage device 278 may comprise, for example, one or more of a solidstate drive, hard disk drive, a magnetic disk drive, an optical diskdrive, or the like.

Video adaptor 280 and I/O interface 288 provide interfaces to coupleexternal input and output devices to the processing unit. Asillustrated, examples of input and output devices include the displaycoupled to the video adapter and the mouse/keyboard/printer coupled tothe I/O interface. Other devices may be coupled to the processing unit,and additional or fewer interface cards may be utilized. For example, aserial interface card (not pictured) may be used to provide a serialinterface for a printer.

The processing unit also includes one or more network interface 284,such as the interface to the OLT or ONU, and others of which maycomprise wired links, such as an Ethernet cable or the like, and/orwireless links to access nodes or different networks. Network interface284 allows the processing unit to communicate with remote units via thenetworks. For example, the network interface may provide wirelesscommunication via one or more transmitters/transmit antennas and one ormore receivers/receive antennas. In an embodiment, the processing unitis coupled to a local-area network or a wide-area network for dataprocessing and communications with remote devices, such as otherprocessing units, the Internet, remote storage facilities, or the like.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods might beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

What is claimed is:
 1. A method comprising: broadcasting, by an opticalline terminal (OLT) to a plurality of optical network units (ONUs), afirst downstream (DS) physical layer (PHY) frame comprising: a firststart time for a first quiet window; and a first allocation identifier(Alloc-ID), wherein the first Alloc-ID indicates that ONUs of a firstgroup of ONUs transmitting at a first supported upstream line rate mayuse the first quiet window and that ONUs of a second group of ONUs nottransmitting at the first supported upstream line rate may not use thefirst quiet window, and wherein the ONUs of the second group of ONUsconfigured to transmit at a second supported upstream line rate; openingthe first quiet window at the first start time; and receiving, from afirst ONU of the first group of ONUs, during the first quiet window, aserial number response.
 2. The method of claim 1, further comprisingbroadcasting, by the OLT to the plurality of ONUs, a second DS PHY framecomprising: a second start time for a second quiet window; and a secondAlloc-ID, wherein the second Alloc-ID indicates that ONUs of the secondgroup of ONUs may use the second quiet window and that ONUs of the firstgroup of ONUs may not use the second quiet window.
 3. The method ofclaim 2, wherein the first Alloc-ID is 1022 and the second Alloc-ID is1023.
 4. The method of claim 1, further comprising broadcasting, by theOLT to the plurality of ONUs, a second DS PHY frame comprising: a secondstart time for a second quiet window; and a second Alloc-ID, wherein thesecond Alloc-ID indicates that ONUs of the second group of ONUs may usethe second quiet window and that ONUs of the first group of ONUs may usethe second quiet window.
 5. The method of claim 4, wherein the secondAlloc-ID is
 1021. 6. The method of claim 1, further comprisingrefraining from communicating, during the first quiet window, with athird group of ONUs already registered to the OLT.
 7. The method ofclaim 1, wherein the first supported upstream line rate is 2.5 G and thesecond supported upstream line rate is 10 G.
 8. The method of claim 1,wherein the first supported upstream line rate is 1.25 G and the secondsupported upstream line rate is 2.5 G.
 9. The method of claim 1, furthercomprising: associating the first ONU with a passive optical network(PON) of the OLT after receiving the serial number response; andprivately communicating, by the OLT with the first ONU, afterassociating the first ONU with the PON.
 10. A method comprising:receiving, by an optical network unit (ONU) from an optical lineterminal (OLT), a first downstream (DS) physical layer (PHY) framecomprising: a first start time for a first quiet window; and a firstallocation identifier (Alloc-ID), wherein the first Alloc-ID indicatesthat ONUs of a first group of ONUs transmitting at a first supportedupstream line rate may use the first quiet window and that ONUs of asecond group of ONUs not transmitting at the first supported upstreamline rate may not use the first quiet window, and wherein the ONUs ofthe second group of ONUs configured to transmit at a second supportedupstream line rate; determining whether an upstream line rate of the ONUis the same as the first supported upstream line rate; transmitting, bythe ONU to the OLT, during the first quiet window, a serial numberresponse upon determining that the upstream line rate of the ONU is thesame as the first supported upstream line rate; and refraining fromtransmitting, by the ONU to the OLT, during the first quiet window, upondetermining that the upstream line rate of the ONU is different than thefirst supported upstream line rate.
 11. The method of claim 10, furtherreceiving, by the ONU from the OLT, a second DS PHY frame comprising: asecond start time for a second quiet window; and a second Alloc-ID,wherein the second Alloc-ID indicates that ONUs of the second group ofONUs may use the second quiet window and that ONUs of the first group ofONUs may not use the second quiet window.
 12. The method of claim 11,wherein the first Alloc-ID is 1022 and the second Alloc-ID is
 1023. 13.The method of claim 10, further comprising receiving, by the ONU fromthe OLT, a second DS PHY frame comprising: a second start time for asecond quiet window; and a second Alloc-ID, wherein the second Alloc-IDindicates that ONUs of the second group of ONUs may use the second quietwindow and that ONUs of the first group of ONUs may use the second quietwindow.
 14. The method of claim 13, wherein the second Alloc-ID is 1021.15. The method of claim 10, further comprising: determining whether theONU is already registered to a passive optical network (PON) of the OLT;and not transmitting, by the ONU to the OLT, during the first quietwindow, upon determining that the ONU is already registered to the PONof the OLT.
 16. The method of claim 10, wherein the first supportedupstream line rate is 2.5 G and the second supported upstream line rateis 10 G.
 17. The method of claim 10, wherein the first supportedupstream line rate is 1.25 G and the second supported upstream line rateis 2.5 G.
 18. The method of claim 10, further comprising: associatingwith a passive optical network (PON) of the OLT after transmitting thefirst serial number response; and privately communicating, by the ONUwith the OLT, after associating with the PON.
 19. An optical lineterminal (OLT) comprising: a processor; and a non-transitory computerreadable storage medium storing programming for execution by theprocessor, the programming including instructions to: broadcast, to aplurality of optical network units (ONUs), a first downstream (DS)physical layer (PHY) frame comprising: a first start time for a firstquiet window; and a first allocation identifier (Alloc-ID), wherein thefirst Alloc-ID indicates that ONUs of a first group of ONUs transmittingat a first supported upstream line rate may use the first quiet windowand that ONUs of a second group of ONUs not transmitting at the firstsupported upstream line rate may not use the first quiet window, andwherein the ONUs of the second group of ONUs configured to transmit at asecond supported upstream line rate; opening the first quiet window atthe first start time; and receiving, from a first ONU of the first groupof ONUs, during the first quiet window, a serial number response.
 20. Anoptical network unit (ONU) comprising: a processor; and a non-transitorycomputer readable storage medium storing programming for execution bythe processor, the programming including instructions to: receive, froman optical line terminal (OLT), a first downstream (DS) physical layer(PHY) frame comprising: a first start time for a first quiet window; anda first allocation identifier (Alloc-ID), wherein the first Alloc-IDindicates that ONUs of a first group of ONUs transmitting at a firstsupported upstream line rate may use the first quiet window and thatONUs of a second group of ONUs not transmitting at the first supportedupstream line rate may not use the first quiet window, and wherein theONUs of the second group of ONUs configured to transmit at a secondsupported upstream line rate; determine whether an upstream line rate ofthe ONU is the same as the first supported upstream line rate; transmit,to the OLT, during the first quiet window, a serial number response upondetermining that the upstream line rate of the ONU is the same as thefirst supported upstream line rate; and refrain from transmitting, tothe OLT, during the first quiet window, upon determining that theupstream line rate of the ONU is different than the first supportedupstream line rate.